The invention relates to a belt pulley for a gear mechanism, in particular for a steering gear, including a cylindrical body having an outer surface on which a toothing made of a plastic material is provided, and a fastening flange which is provided with fastening openings. The invention further relates to an assembly including a gear nut and such a belt pulley.
A belt pulley of the type initially mentioned is known from DE 10 2004 058 963 A1. It is coupled to a recirculating ball nut so as to prevent relative rotation and relative displacement, the recirculating ball nut having, in turn, a screw coupled thereto. A toothed belt can engage with the toothing on the outer surface of the belt pulley, the toothed belt running over a further belt pulley which, in turn, is coupled to a drive motor. The gear mechanism formed in this way is employed in particular in electromechanically operated rack-and-pinion steering systems in motor vehicles.
In this known belt pulley, the cylindrical body is made from sheet metal, and the toothing is configured as a plastic part on the outer surface of the cylindrical body. To ensure a connection with the ball nut in a manner so as to prevent relative rotation, the fastening flange may be provided with a plurality of openings through which fastening elements extend which engage into openings on the periphery of the recirculating ball nut.
A similar structure is disclosed in DE 10 2006 059 946 A1. Here, too, a cylindrical body is used which has a toothing applied on its outside. Light metal alloys or fiber composite materials may be used for the base body. The toothing is made from a thermosetting plastic. This is intended to generally achieve a weight saving.
Also already known from the prior art are belt pulleys which are made entirely from a plastic material. Examples thereof are found in DE 10 2007 049 114 A1 and WO 2011/117099 A1. But with these belt pulleys it is no longer possible to transmit the torques between the belt pulley and the gear nut via a fastening flange. Rather, shaft-hub connections are employed which make use of a tongue and groove or of spiral pins.